private static void EncodeInternal(Stream destination, byte[] buffer, long slidingWindow, long recLength, long size)
{
UInt16BE_NE_H_OutputBitStream bitStream = new UInt16BE_NE_H_OutputBitStream(destination);
MemoryStream data = new MemoryStream();
if (size > 0)
{
long bPointer = 2, longestMatchOffset = 0;
bitStream.Push(false);
NeutralEndian.Write1(data, buffer[0]);
NeutralEndian.Write1(data, buffer[1]);
while (bPointer < size)
{
long matchMax = Math.Min(recLength, size - bPointer);
long backSearchMax = Math.Max(bPointer - slidingWindow, 0);
long longestMatch = 2;
long backSearch = bPointer;
do
{
backSearch -= 2;
long currentCount = 0;
while (buffer[backSearch + currentCount] == buffer[bPointer + currentCount] && buffer[backSearch + currentCount + 1] == buffer[bPointer + currentCount + 1])
{
currentCount += 2;
if (currentCount >= matchMax)
{
// Match is as big as the look-forward buffer (or file) will let it be
break;
}
}
if (currentCount > longestMatch)
{
// New 'best' match
longestMatch = currentCount;
longestMatchOffset = backSearch;
}
} while (backSearch > backSearchMax); // Repeat for as far back as search buffer will let us
long iCount = longestMatch / 2; // Comper counts in words (16 bits)
long iOffset = (longestMatchOffset - bPointer) / 2; // Comper's offsets count in words (16-bits)
if (iCount == 1)
{
// Symbolwise match
Push(bitStream, false, destination, data);
NeutralEndian.Write1(data, buffer[bPointer]);
NeutralEndian.Write1(data, buffer[bPointer + 1]);
}
else
{
// Dictionary match
Push(bitStream, true, destination, data);
NeutralEndian.Write1(data, (byte)(iOffset));
NeutralEndian.Write1(data, (byte)(iCount - 1));
}
bPointer += iCount * 2; // iCount counts in words (16-bits), so we correct it to bytes (8-bits) here
}
}
Push(bitStream, true, destination, data);
NeutralEndian.Write1(data, 0);
NeutralEndian.Write1(data, 0);
bitStream.Flush(true);
byte[] bytes = data.ToArray();
destination.Write(bytes, 0, bytes.Length);
}
internal static void Encode(Stream source, Stream destination)
{
int size_bytes = (int)(source.Length - source.Position);
byte[] buffer_bytes = new byte[size_bytes + (size_bytes & 1)];
source.Read(buffer_bytes, 0, size_bytes);
int size = (size_bytes + 1) / 2;
ushort[] buffer = new ushort[size];
for (int i = 0; i < size; ++i)
{
buffer[i] = (ushort)((buffer_bytes[i * 2] << 8) | buffer_bytes[(i * 2) + 1]);
}
/*
* Here we create and populate the "LZSS graph":
*
* Each value in the uncompressed file forms a node in this graph.
* The various edges between these nodes represent LZSS matches.
*
* Using a shortest-path algorithm, these edges can be used to
* find the optimal combination of matches needed to produce the
* smallest possible file.
*
* The outputted array only contains one edge per node: the optimal
* one. This means, in order to produce the smallest file, you just
* have to traverse the graph from one edge to the next, encoding
* each match as you go along.
*/
LZSSGraphEdge[] node_meta_array = new LZSSGraphEdge[size + 1];
// Initialise the array
node_meta_array[0].cost = 0;
for (int i = 1; i < size + 1; ++i)
{
node_meta_array[i].cost = int.MaxValue;
}
// Find matches
for (int i = 0; i < size; ++i)
{
int max_read_ahead = Math.Min(0x100, size - i);
int max_read_behind = Math.Max(0, i - 0x100);
// Search for dictionary matches
for (int j = i; j-- > max_read_behind;)
{
for (int k = 0; k < max_read_ahead; ++k)
{
if (buffer[i + k] == buffer[j + k])
{
int distance = i - j;
int length = k + 1;
// Update this node's optimal edge if this one is better
if (node_meta_array[i + k + 1].cost > node_meta_array[i].cost + 1 + 16)
{
node_meta_array[i + k + 1].cost = node_meta_array[i].cost + 1 + 16;
node_meta_array[i + k + 1].previous_node_index = i;
node_meta_array[i + k + 1].match_length = k + 1;
node_meta_array[i + k + 1].match_offset = j;
}
}
else
{
break;
}
}
}
// Do literal match
// Update this node's optimal edge if this one is better (or the same, since literal matches usually decode faster)
if (node_meta_array[i + 1].cost >= node_meta_array[i].cost + 1 + 16)
{
node_meta_array[i + 1].cost = node_meta_array[i].cost + 1 + 16;
node_meta_array[i + 1].previous_node_index = i;
node_meta_array[i + 1].match_length = 0;
}
}
// Reverse the edge link order, so the array can be traversed from start to end, rather than vice versa
node_meta_array[0].previous_node_index = int.MaxValue;
node_meta_array[size].next_node_index = int.MaxValue;
for (int node_index = size; node_meta_array[node_index].previous_node_index != int.MaxValue; node_index = node_meta_array[node_index].previous_node_index)
{
node_meta_array[node_meta_array[node_index].previous_node_index].next_node_index = node_index;
}
/*
* LZSS graph complete
*/
UInt16BE_NE_H_OutputBitStream bitStream = new UInt16BE_NE_H_OutputBitStream(destination);
MemoryStream data = new MemoryStream();
for (int node_index = 0; node_meta_array[node_index].next_node_index != int.MaxValue; node_index = node_meta_array[node_index].next_node_index)
{
int next_index = node_meta_array[node_index].next_node_index;
int length = node_meta_array[next_index].match_length;
int distance = next_index - node_meta_array[next_index].match_length - node_meta_array[next_index].match_offset;
if (length != 0)
{
// Compressed
Push(bitStream, true, destination, data);
NeutralEndian.Write1(data, (byte)-distance);
NeutralEndian.Write1(data, (byte)(length - 1));
}
else
{
// Uncompressed
Push(bitStream, false, destination, data);
BigEndian.Write2(data, buffer[node_index]);
}
}
Push(bitStream, true, destination, data);
NeutralEndian.Write1(data, 0);
NeutralEndian.Write1(data, 0);
bitStream.Flush(true);
byte[] bytes = data.ToArray();
destination.Write(bytes, 0, bytes.Length);
}